edgeql: Add converter functions for multiple data types.

The `to_str` function is meant to be like a cast when called
without the format parameter.

`to_str` usage with `json` scalars is not equivalent to casting, it is
producing a string representation of JSON. The inverse function `to_json`
is therefore parsing a string, not casting either:
- `str_to_json` becomes `to_json`
- `json_to_str` becomes `to_str`

Add various date and time converter functions.

edb/lang/graphql/translator.py

@@ -118,7 +118,7 @@ def visit_Document(self, node):
         for el in eql[0].result.elements:
             # swap in the json bits
             if (isinstance(el.compexpr, qlast.FunctionCall) and
-                    el.compexpr.func == 'str_to_json'):
+                    el.compexpr.func == 'to_json'):
                 name = el.expr.steps[0].ptr.name
                 el.compexpr.args[0].arg = qlast.StringConstant.from_python(
                     json.dumps(gqlresult.data[name], indent=4))

edb/lang/graphql/types.py

@@ -572,7 +572,7 @@ def get_template(self):
         '''
 
         if self.dummy:
-            return parse_fragment(f'''str_to_json("xxx")'''), None, None
+            return parse_fragment(f'''to_json("xxx")'''), None, None
 
         eql = parse_fragment(f'''
             SELECT {self.edb_base_name} {{

edb/lib/std/20-genericfuncs.eql

@@ -44,7 +44,7 @@ CREATE FUNCTION
 std::len(array: array<anytype>) -> std::int64
 {
     FROM SQL $$
-    SELECT COALESCE(array_length("array", 1), 0)::bigint
+    SELECT cardinality("array")::bigint
     $$;
 };
 

edb/lib/std/30-datetimefuncs.eql

@@ -84,3 +84,21 @@ std::timedelta_get(dt: std::timedelta, el: std::str) -> std::float64
     SELECT date_part("el", dt)
     $$;
 };
+
+
+CREATE FUNCTION
+std::datetime_trunc(dt: std::datetime, unit: std::str) -> std::datetime
+{
+    FROM SQL $$
+    SELECT date_trunc(unit, dt)
+    $$;
+};
+
+
+CREATE FUNCTION
+std::timedelta_trunc(dt: std::timedelta, unit: std::str) -> std::timedelta
+{
+    FROM SQL $$
+    SELECT date_trunc(unit, dt)
+    $$;
+};

edb/lib/std/30-jsonfuncs.eql

@@ -54,21 +54,3 @@ std::json_get(
     )
     $$;
 };
-
-
-CREATE FUNCTION
-std::json_to_str(json: std::json) -> std::str
-{
-    FROM SQL $$
-    SELECT "json"::text
-    $$;
-};
-
-
-CREATE FUNCTION
-std::str_to_json(str: std::str) -> std::json
-{
-    FROM SQL $$
-    SELECT "str"::jsonb
-    $$;
-};